“Show me your friends and I’ll show you who you are,” the saying goes. Dr Nicholas Christakis, 47, a physician and sociologist at Harvard University now says we may as well show the friends of our friends.

After studying a database of some 5,000 people over the course of 20 years, Christakis and collaborator James H. Fowler found that social networks can transmit things like obesity or smoking but also moods like happiness. More amazingly, Christakis claims, emotions can travel even between people who don’t know each other directly. For that finding, he was included in the TIME’s “100 most influential list” for 2009. The Greek American scientist talked to Athens Plus explaining, among other things, why we shouldn’t quite expect the ripple effect reaching our office cubicles.

First of all congratulations for making the list of the 100 most influential people of TIME magazine. Do you think this will help your work in any way?

This sort of unexpected recognition draws attention to this kind of work. And the kind of work we’re doing is to study social networks. We are very interested in why people have networks and what purpose networks serve. It is pretty obvious that people are influenced by the people they are directly connected to, but what is much more interesting is how people are influenced by people they’re not connected to. We are not interested in person-to-person transmission but person-to-person-to-person – like three degrees of influence.

Last week Sydney hosted a conference examining the causes of happiness. Do you think some people are born happier than others?

Yes, I do. It’s not totally genetic, but there is no doubt that there are disposition. Part of the variation of who’s happy and who’s not can be explained by genes.

Is happiness measurable? Have you based your research on a certain definition of happiness or on people’s statement of being happy?

We do use a standard measure of happiness. There are different ways of measuring these things, but I do think it’s possible. Human beings, we observe all kinds of subjective things all the time; we see whether people are in pain or not, we draw conclusions about people’s honesty or badness all the time.

According to a recent report, Denmark, Finland and the Netherlands rate at the top of the world’s happiest places. Could your theory explain why people in some countries are happier than others?

Our work is about social networks. We look at how all kinds of things, ideas, behaviors, emotions spread in social networks. It’s easy to imagine how things like germs or money move across social ties. But we are interested in how unconventional things like hate or desire, behaviors or emotions move across social networks.

Could it be that happy or obese people for that matter are simply drawn to each other?

Of course that’s a possible explanation, but our work takes that into account. There’s a variety of possible explanations for this clustering of similar individuals within networks. One is a good Greek word, “homophily,” which is birds of a feather flocked together. So people who exercise hang out with people who exercise, people who are happy hang out with people who are happy. Another possible explanation is that some other factors that make people have similar traits in unison for example maybe there is an economic recession and that makes a lot of people unhappy. If you and I are friends and we both work in the same factory and lose our jobs we’re both going to become unhappy but not because I made you unhappy but because we were exposed to this other factor. And a third possibility is that my unhappiness causes your unhappiness and it is important in these kinds of analyses to take all of those possibilities into consideration.

You have said that the spread of happiness is more geographically limited than the spread of obesity is that so?

Our interest is in how things spread in social networks. But not everything that spreads in a network spreads by the same mechanism. And we think that emotions require face-to-face contact. And that has to be some kind of interaction. So therefore people who live far apart from each other may not come into contact with each other.

What about Schadenfreude. Does that contract your theory in any way?

For sure there is Schadenfreude. But on average there is more of the opposite. In our work we found that happiness does not spread among coworkers. We thought that this might be because of Schadenfreude.

Back to social networks now. You have said that the architecture of social networks and our position in them is genetically affected. Are you saying something other than that being shy or outgoing affects your status in society?

Yes we are. Most people wouldn’t be surprised if you said that some people had many friends and some people had few friends, some people are shy and some people are outgoing and that this has a partially genetic basis. We all know people who are from birth very shy for example. So if I said that some people had two friends and some people had ten friends the fact that that had a partially genetic basis would not be surprising. But here is something that should surprise you. I might have four friends and you might have four friends but my four friends might all know each other and your four friends might not know each other. This is something called transitivity in social networks. And it turns our that you and I would have different genes. What we find is something very interesting. We find that if Tom, Dick and Harry are in a room, whether Dick and Harry know each other depends not just on Dick and Harry’s genes but also on Tom’s genes. It’s very bizarre. If Dick and Harry know each other depends on a third person’s genes. And we think the reason is that people have a genetic tendency to introduce their friends. Some people are more likely to introduce their friends than others.

Where does religion fit in all this? Would you say that religious belief can be contagious like happiness or a habit?

I believe that religious beliefs spread, absolutely. That’s one way. Another way is one of the functions of religion is to bind social networks together. So if you and I both believe in the same god, I can feel connected to you even if I don’t know you. It’s like we’re friends of a friend.

Have you been able to draw any significant patterns from online social networks like Facebook or Twitter?

We’ve been doing some work with Facebook. We’ve looked at for instance smiling on people’s Facebook profiles. People who smile in their profile pictures have more friends who smile in their profile pictures and also have more friends in general.

Some scientists have criticized you of not having replicated your findings.

That’s not true. We’ve replicated our findings in several ways and other scientists have also replicated our findings. So for example our obesity findings we published a replication in the journal of Health Economics and our happiness findings have been replicated by several other groups both at Warrick and Oxford University in England.